Vehicles such as combines, construction fork trucks, and road pavers, are today quite often equipped with wheels used for steering the vehicle and which are also driven by a fluid or hydraulic motor. It is desirable to equip the steerable wheels with hydraulic powered motors so as to assist in driving the vehicle and obtaining better performance in rough and slippery terrain, such as muddy fields and construction sites.
Typically, as shown in FIG. 1, a hydraulic motor M is pivotally mounted on a vehicle chassis C for pivotal movement about axis X. A wheel W having a rim R is detachably attached to the motor shaft S and has a vertical centerline L. Hydraulic fluid at a substantially high pressure is selectively provided to motor M via lines (not shown) for selectively driving wheel W as needed. Additionally, tie rods are pivotally connected to motor M and are selectively caused to move via the vehicle steering wheel for selectively pivoting motor M and wheel W about axis X and thereby steering the wheel and providing control of the vehicle in the desired direction.
Many different hydraulic motors M are available for use in such applications. In general, these motors include a bearing assembly circumscribing shaft S and located closest to the portion of shaft S extending out of motor M toward rim R. The motor M further includes a piston drive assembly next to the bearing assembly and a fluid distribution assembly next to the piston drive assembly. Thus, the piston drive assembly is located inbetween the bearing assembly and the drive assembly. The distribution assembly distributes the high pressure fluid to the plurality of pistons in the drive assembly which under proper timing, force rollers against a cam and thereby drive shaft S for turning wheel W. The distribution of hydraulic fluid and overall operation of such hydraulic motors is well known and such motors are currently available from sources such as Poclain, Rexroth, Deere & Company and Valmet.
Unfortunately, the prior art steering wheel drive assemblies have shortcomings and drawbacks. Because of the longitudinal length and diameter of motor M, it becomes quite difficult to fit the assembly within the cup-shaped rim R and, as a consequence, the design requires the pivot to be about axis X which is at an angle with respect to the centerline L of wheel W. As a further consequence, there is an undesirable swing distance equal to the distance between axis X and centerline L. As wheel W and motor M are pivoted about axis X, the upper end of wheel W tends to swing with respect to axis X. Furthermore, the prior steering wheel drive assemblies require the diameter of the wheel W to be matched to the assembly so that the intersection of axis X and centerline L occurs generally at the point of contact between wheel W and the ground. If the wheel diameter is not properly matched, the lower end of the wheel will also be subjected to a swing movement during turning. Further yet, in view of the swing distance between axis X and centerline L, the overall steering angle (the overall angle that wheel W can be pivoted about centerline L) is generally limited and, a generally larger vehicle tire envelope is required for overall smaller steering angles.
Accordingly, a need exists for a steering wheel drive assembly that improves the prior art assemblies and provides a shorter or no swing distance for all different diameter wheels and which provides a larger steering angle while requiring an overall small vehicle tire envelope.